The traditional approach of conducting communication with an implantable medical device (IMD) has been through usage of inductive telemetry. Nowadays, the communication technology within the field of IMDs is moving away from inductive telemetry towards radio frequency (RF) based telemetry or communication.
RF telemetry has several advantages over inductive telemetry including, for instance, higher bit rates and longer range. However, a drawback is that RF telemetry generally requires more power. IMDs are typically battery driven and therefore have limited operation life dictated by the power consumption of the IMDs. Utilizing RF telemetry as the communication protocol consequently causes an impact to the longevity of the IMDs.
In order to at least partly solve this problem of increased power consumption for RF-based communication sessions between IMDs and non-implantable communication units or modules, algorithms for reducing power have been developed. An example of such an algorithm is denoted power save and involves regularly turning off the radio equipment in the IMD for a certain time period, typically 20-30 ms, during a communication session. The power save algorithm is mainly based on the stream of intracardiac electrogram (IEGM) data that is sent periodically in a burst-like manner from the IMD. For instance and depending on the particular device design, IEGM samples can be produced by the IMD every 7.8125 ms. The IMD then preferably buffers a number of such IEGM samples, such as six, prior transmission. The buffering of IEGM samples yields a periodicity of, in this example, 6.times.7.8125=46.875 ms for the IEGM messages sent from the IMD to the non-implantable communication unit. Power saving can therefore be performed during those periods when the IMD buffers IEGM samples.
Though the power save algorithm reduces power consumption by turning off the IMD radio equipment several times during an ongoing communication session it may also, as a drawback, prolong the communication session. The net result may therefore in some cases not be a power reduction but actually increased total energy consumption for the whole communication session and thereby reduced longevity of the IMD.
U.S. Pat. No. 6,647,298 relates to saving power during the communication between an IMD and a non-implantable communication unit. The power saving is accomplished by selectively switching on and off the receiver of the IMD based on whether received signal strengths exceed a discriminator threshold.
US 2007/0150028 discloses a remote monitoring device interrogating an IMD on an intermittent basis over a wireless telemetry link, with interrogations being performed either according to a programmed schedule or upon receiving a command to do so via a user interface. Power management can optimize RF telemetry usage of the IMD by combining interrogations scheduled to occur at or near the same time into a single communications session.